Guidebars for chainsaws are normally provided with oil holes at the clamping end, through which oil is pumped into the bottom of the chain groove on the upper side of the guidebar where the chain has left the drive sprocket and moves forward towards the nose part of the guidebar. The parts of the guidebar which need lubrication are the underside, where the chain during sawing is pressed against the guidebar, and the nose part, where the chain becuase of its curvature exerts high pressure against the nose sprocket, or on older guidebar types on the hardened edge of the guidebar. Because of the long distance from the oil hole to the nose part and the underside, the lubricating oil takes a long time to reach there, especially if sawdust has collected at the bottom of the chain grooves.
Chainsaws are increasingly often used as components of vehicle-borne machines for felling and bucking of tree trunks, and then the running conditions differ from hand-held chainsaws, in that the guidebar for each cut is active for a much shorter period with much higher chain velocity and a much higher force against the tree trunk. There is a strong need of improved lubrication, and at the same time the time available is less, since the oil flow can not be maintained the whole time but only during the cut proper, as is described in the Swedish Pat. No. 380,996.
Under these circumstances it is desirable to ensure that the oil immediately reaches the nose part, which can be achieved by not connecting the oil holes to the upper rear end of the chain groove, but leading the oil forwards through closed channels in the guidebar to the parts needing lubrication. Several such designs are known, where an oil channel leads to the recess for the nose sprocket, such as French Patent No. 756.690 and U.S. Pat. No. 2,992,660, or to the nose sprocket bearing, such as U.S. Pat. No. 3,044,506 and Swedish Patent No. 438,812, or to the chain groove at a point closer to the nose part, such as German Patent No. 908,296, U.S. Pat. Nos. 2,913,020 and 2,748,810, and Soviet Union No. 406.725. None of these will ensure that the oil reaches all surfaces that need lubrication immediately before the lubrication is needed.
The present invention concerns a guidebar with closed oil channels, arranged to lubricate the inside of the chain just before it starts sliding against the underside of the guidebar, as well as the supporting teeth of the nose sprocket just before they intermesh with the chain.
According to the invention the guidebar is provided with closed channels leading to the corner where the chain groove of the underside meets the nose sprocket recess. The oil is thereby sprayed onto the inside of the chain at the short stretch where it is lifted from the sprocket but has not yet started sliding against the edge of the guidebar, as well as onto the sprocket teeth in the sector where they are freely accessible.